We've all seen the Claire McCaskill's campaign ad from last year with Michael J. Fox, right? In case you haven't, it's on YouTube.
The obvious enthymeme here is Vote for Claire McCaskill because she'll support stem cell research.
But certainly there's a lot more going on. Why, for instance do we need a famous actor like Michael J. Fox in order to tell us that McCaskill is pro-stem cell research? We need only look at Jim Talent's voting record to see that he (as Fox says) not only opposes funding, but also tried to make the research illegal in Missouri.
So Fox is here to be a sign of what stem cell research can do. McCaskill appeals to our pathos. Seeing the star of Teen Wolf unable to control his movements, we're moved to pity and we want to believe that stem cell research can help real people that we feel a connection with.
So the ad contains the premise that supporting stem cell research can help treat people like Michael J. Fox. And the premise that supporting Claire McCaskill is supporting stem cell research. One unstated assumption is that we ought to support stem cell research if it helps people like Michael J. Fox. Another is that supporting stem cell research should be done through electing advocates to the US government.
The ad actually ignores the main claim of those who oppose (human embryonic) stem cell research: that it destroys human life (or potential human life, or the sanctity of human life). The question is, does the ad address those who accept that claim? If so, then it has to also contain the assumption that the destruction of embryos is justifiable, either because they are not life or because they are less important than people like Michael J. Fox. That, or McCaskill hopes by not mentioning the issue, people will forget about that objection because the painful-to-watch image of a familiar face and voice behind erratic movements caused by over-medication is much stronger than that of petri dishes in a lab.